Avoiding "is not defined" errors with Pylance and VSCode

[sgmoore]

Does anyone use Microsoft's Pylance static type checker in VSCode and know how to disable this type of error.

For example, given the following snippet

# noinspection PyUnreachableCode
if False :
    load_translations = _ = ngettext = lambda x=None, y=None, z=None: x

load_translations()

The first few lines are enough to stop ruff and mypy from complaining about the method call but not Pylance which displays an error like

"load_translations" is not defined Pylance (reportUndefinedVariable)

I know I have three options
1) Disable pylance
2) Disable this type of error across the whole project
3) Pollute the codebase by adding "# type: ignore" to hundreds of lines.

But I would prefer not to have do any of these and was wondering if there was a better way?

[kovidgoyal]

Why do you need to do that at all? Just import those functions explicitly, like this

from calibre.utils.localization import gettext as _, ngettext, load_translations

[sgmoore]

Originally Posted by kovidgoyal

Why do you need to do that at all? Just import those functions explicitly, like this

from calibre.utils.localization import gettext as _, ngettext, load_translations

I guess the main reason is that I am also reluctant to change code that I don't fully understand (and it's probably obvious that I'm not the original author of the code).

(Although I have been a programmer for several decades, I would still consider myself a beginner as far as python is concerned and they are many things that I don't fully understand.)

In particular, looking at the git history, this code used to call the load_translations and _ methods without actually importing them and I have no idea how or where it finds these methods and hence what they did.

Later it was amended and there is now a section of code which does

try:
    from calibre.utils.localization import _ as _c
    from calibre.utils.localization import ngettext as ngettext_c
except ImportError:
    # fallback to global _ for calibre<6.12
    _c = _
    ngettext_c = ngettext

This I mostly understand, but note :

It does not import load_translations from calibre.utils.localization and I would presume that means it is still loading another method from somewhere.

Also, the fact that it renames calibre's _ method as _c can only mean that there was a deliberate decision to use the original _ method in some places and the calibre version in others and I have no idea why.

[kovidgoyal]

Those are all functions that were defined as globals in calibre a long time ago. _ and gettext and ngettext can now be imported perfectly safely. If you are worried about doing so for compat reasons you can do the following:

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from calibre.utils.localization import ...
else:
    the original code

This should work with all type checkers. As for load_translations() that's specific to calibre plugins and is documented in the manual https://manual.calibre-ebook.com/creating_plugins.html